1. Field of the Invention
The present invention relates to guide wires and catheters used for surgical operations, and more specifically, to catheters such as fiber optic catheters used for illuminating and ablating intravascular regions and to guide wires for positioning such catheters.
2. Description of the Related Art
Angioplasty, a therapeutic medical procedure in which a catheter or the like is inserted into a blood vessel to increase blood flow, has developed in many cases as a safer, less expensive alternative to by-pass surgery. The first catheters for angioplasty were balloon catheters built up around a steerable guide wire core. The catheter is inserted into the vessel until the position of the balloon corresponds to the position of an obstruction in the blood vessel, and then the balloon is pressurized, opening the artery and increasing blood flow.
Typically, a steerable guide wire passes through the balloon catheter and is able to move independently of the catheter. The guide wire, of relatively small diameter, is inserted into the patient's blood vessel and moved into proper position past the obstruction. Then the balloon catheter, surrounding the guide wire, is advanced along the guide wire until the catheter is in proper position, with the balloon at the obstruction. This guide wire and catheter combination allows the guide wire to be inserted into place before the catheter thus making it easier to position the catheter.
Catheters containing optical fibers have also been constructed for insertion into veins and arteries. Energy is conducted along the fibers to irradiate internal parts of the body for diagnostic and surgical purposes. There are also many other medical applications in which it is desirable to deliver energy, such as laser energy, through an optical fiber or similar waveguide device disposed in a body cavity for treatment or diagnosis. These include the ablation of tissue such as plaque (e.g., angioplasty) and tumors, the destruction of calculi and the heating of bleeding vessels for coagulation. The lasers used may produce either pulsed or continuous-wave light of wavelengths ranging from the ultra-violet to the infra-red. Like balloon catheters, laser catheters are generally used with a guide wire to steer and position the catheter in the patient's body.
Laser and balloon techniques may be combined in an angioplasty process. An example of such a technique is given in U.S. Pat. No. 4,834,093 to Littleford et al. In this patent, a laser catheter is introduced into an intravascular area with the aid of a guide wire. The catheter/guide wire combination is positioned near a vascular occlusion, and the catheter is used to deliver laser energy to the occlusion to ablate a channel through the occlusion. While leaving the guide wire in position, the laser catheter is withdrawn from the patient and a balloon catheter is slid down the guide wire to the treatment site. The balloon catheter is inflated to dilate the remaining occluded area. When the catheter and guide wire are withdrawn, the previously occluded area remains dilated; thus, blood flow through the region is increased.
U.S. Pat. No. 4,854,315 to Stack et al. shows a laser catheter employing a related technique. In the Stack et al. device, a guide wire is used to position a first laser catheter near an intravascular obstruction. The first catheter is used to ablate a channel through the obstruction and to better position the device within the vessel. A second, larger catheter concentrically disposed on the first catheter is slid down the first catheter/guide wire assembly to the obstruction and continues the ablation process by eliminating the peripheral regions of the obstruction. In this manner, a level of blood flow comparable to that achieved through balloon dilation may be realized.
U.S. Pat. No. 4,739,768 to Engelson discloses an infusion catheter usable in conjunction with a guide wire. The catheter has a relatively stiff inner proximal member and a more flexible outer member covering at least a portion of the inner member and projecting therefrom at its distal end. The bifurcated stiffness profile of the infusion catheter aids in the tracking and placement of a conventional guide wire threaded therein.
In the above prior art designs, the shape and nature of the vascular occlusion will not always permit a guide wire to be positioned so that a laser catheter can be accommodated for ablation. A total vascular occlusion may prevent a guide wire from crossing the occlusion. If the occlusion cannot be crossed by conventional techniques, such as dottering the wire through the occlusion, by-pass surgery is required to reestablish blood flow through the vessel.
Though a laser catheter can ablate the occlusion and thus allow the surgical assembly to pass, its relatively large diameter prohibits adequate positioning within the vessel to perform the ablation process. Moreover, the large size of the guide wire/catheter combination may traumatize some vessels or otherwise limit the use of the device.